Date: 01 Jul 2012
This guide provides information to assist in decision making for control of western flower thrips (WFT) in capsicums; cucumbers; culinary herbs; eggplant; lettuce; ornamentals; parsley and coriander; silverbeet; spring onions and shallots; stone fruit; strawberries; tomatoes; and snow peas and sugar snap peas. It includes:
WFT can cause damage to crops by feeding on them, and can spread tomato spotted wilt virus (TSWV) in crops.
Insecticides alone are not enough to beat WFT. The following cultural control advice should be used, together with a chemical strategy, to effectively manage WFT, and avoid infections of TSWV.
WFT is a pest that readily acquires resistance to insecticides. For this reason it is important to avoid dependence on a single chemical.
It is also important that growers make their own judgment as to the suitability, effectiveness and safety of the chemicals for the intended use, and the effect that use of the chemical may have on trade, and do so at their own risk.
Always read the label
Users of agricultural (or veterinary) chemical products must always read the label and any Permit before using the product, and strictly comply with the directions on the label and the conditions of any Permit. Users are not absolved from compliance with the directions on the label or the conditions of the Permit by reason of any statement made or not made in this publication.
|Crop||Effects of WFT||Effects of TSWV|
|Capsicums||Silvering on surface and corkiness under the calyx. Ghost spotting more rarely.||Shirting and tip yellowing of plant. Multi-coloured ringed fruit.|
|Cucumbers||Deformities including curled fruit and silvering on leaves.||Does not show symptoms in cucumbers, but can be spread to other crops.|
|Lettuce||Scarring on leaf undersides.||Wilting of leaves.
Browning of tissues.
|Ornamentals||Scarring, silvering, flecking, distortion.||Effects are crop-specific.|
|Stone fruit||Silver russetting on fruit in the weeks just prior to harvest.
Deformed fruit resulting from WFT feeding during fruit formation.
|Stone fruit are not affected by TSWV.|
|Strawberries||Russetting on fruit surfaces or around seeds.
Other symptoms that look like frost damage, boron deficiency or sun scald.
|Strawberries are not affected by TSWV.|
|Tomatoes||Silvering on lower leaves. Occasionally scarring on fruit.||Wilting and bronzing of leaves.
Yellow splotches or concentric rings on ripe fruit.
It is important to monitor your crops or orchard to check if WFT is present because it can easily be confused with other less damaging species of thrips. Monitor using yellow sticky traps and crop/orchard inspections.
Adult and larval stages of WFT can be effectively killed by insecticides, but the eggs (laid inside leaf tissue) and pupae (mostly in soil) are protected from sprays. (See the diagram below of the life cycle of WFT.) For this reason three sprays are recommended to cover the time taken for eggs to hatch into larvae and for pupae to develop into adults.
A series of three sprays of the same chemical a few days apart will be effective for killing the majority of thrips.
The interval between applications varies with temperature. In cooler regions or at cooler times of the year
Important note on applying consecutive sprays, and chemical resistance
Reduce the chance of WFT becoming resistant. Apply three consecutive sprays of the same chemical and then alternate to a different chemical group for the next series of sprays. There must be at least a 3 week break
Follow product label directions for the minimum interval between successive applications.
You should continue to monitor numbers of WFT so you know when to apply another series of sprays. If WFT are building up on sticky traps or you see many WFT on your plants, or fresh damage is visible then consider spraying again.
However, if the same insecticide is always used to control WFT, the thrips will become resistant and the chemical will no longer be effective. Superscript in Table 1 indicates possible resistance already present in the WFT population.
Chemicals approved by the APVMA for off-label use, and chemicals registered for use against thrips or WFT, in:
N.B. To see all chemical control possibilities see both generic and specific listings, e.g. berry fruit and strawberry; leafy vegetables and lettuce.
For more information about WFT see the Thrips section of the NSW DPI website.
Author: Grant Herron, Marilyn Steiner, Bettina Gollnow, Stephen Goodwin